Since electric sewing can accurately control a sewing speed, increase the throughput and improve the sewing quality, most industrial sewing machines and household sewing machines have been equipped with electric motors to become electric sewing machines. A sewing mechanism of the electric sewing machine is typically driven by the motor via a belt. Generally, when stopping a sewing operation of the sewing machine, it is expected that a needle of the sewing mechanism can be held right at its topmost position, such that a maximum space exists between the needle and an underneath seat of the sewing machine to allow easy movement of a fabric being sewn or change of a thread being used, etc. Therefore, an accurate stopping position control is required for the sewing machine.
Due to cost considerations, a motor for a sewing machine is generally an induction motor that can not perform a positioning control itself. Moreover, as it is usually necessary to resume high-speed sewing within a very short period of time after temporarily stopping the sewing operation, the main motor for the sewing machine must be always kept rotating at a high rotation speed. Accordingly, the motor system for the sewing machine is often provided with an additional control system and mechanism for the purpose of accurately positioning the needle and immediately resuming high-speed sewing.
FIG. 6 is a cross-sectional view of a conventional stopping position control motor system 5 for a sewing machine. As shown in FIG. 6, the conventional stopping position control motor system 5 comprises a main motor unit 51, a clutch unit 52, and a deceleration unit 53. The main motor unit 51 comprises a motor casing 515, a stator 511 and a rotor 512 that are accommodated within the motor casing 515, a motor main shaft 513, and a motor flywheel 514 fixed on a front end of the motor main shaft 513. The clutch unit 52 comprises a drawbar 525 pivoted on the motor casing 515, a sliding sleeve 521 that can slide forwardly and backwardly by actuation of a front portion of the drawbar 525, an output shaft 522 rotatably connected to the sliding sleeve 521, a clutch disk 523 fixed on a back end of the output shaft 522, and a friction pad 524 attached to a surface of the clutch disk 523 facing toward the motor flywheel 514. Moreover, a belt pulley (not shown) for coupling a belt can be provided on a front end of the output shaft 522 to drive a sewing mechanism (not shown) of the sewing machine through the belt. The deceleration unit 53 comprises a large-sized gear disk 532 supported on the motor casing 515 by a large-sized bearing 531, a friction pad 533 attached to a surface of the large-sized gear disk 532 facing toward the clutch disk 523, a deceleration motor shaft 534 having a worm gear and for driving the large-sized gear disk 532 to rotate at a second rotation speed (low rotation speed), a deceleration motor (not shown) for driving the decelerating motor shaft 534, and a brake mechanism (not shown) provided on a back end of the decelerating motor.
When power is turned on, the rotor 512 and the stator 511 of the main motor unit 51 are actuated by the power to drive the motor main shaft 513 and the motor flywheel 514 to rotate at a first rotation speed (high rotation speed). When a sewing operation of the sewing machine is to be carried out, the drawbar 525 is pulled upwardly in FIG. 6 to actuate the sliding sleeve 521 to move to a contact position and actuate the output shaft 522 and the clutch disk 523 to move backwardly, such that the clutch disk 523 abuts against and presses the motor flywheel 514. As a result, the clutch disk 523 is immediately driven by a friction force between the friction pad 524 and the motor flywheel 514, making the clutch disk 523 and the output shaft 522 start rotating at the first rotation speed promptly and thus driving the sewing mechanism of the sewing machine to perform the sewing operation at a first speed (high speed). When the sewing operation is to be stopped, the drawbar 525 is pushed downwardly in FIG. 6 to actuate the sliding sleeve 521 to move to a separation position and drive the output shaft 522 and the clutch disk 523 to move forwardly, such that the clutch disk 523 is disengaged from the motor flywheel 514 and is coupled to the large-sized gear disk 532 by a friction force between the friction pad 533 and the clutch disk 523. Since the large-sized gear disk 532 rotates at the second rotation speed (low rotation speed), the sewing operation is carried out by the sewing mechanism of the sewing machine at a second speed (low speed). Then, when the needle of the sewing mechanism reaches its topmost position, a signal is sent from a sensor such as a magnetic switch or photo sensor (not shown) to turn off the power supplied to the deceleration motor and actuate the brake mechanism at the same time to stop the rotation of the deceleration motor, such that the rotation of the large-sized gear disk 532 and the sewing operation are terminated.
However, since the large-sized bearing 531 has a relatively large size and the large-sized gear disk 532 needs to cooperate with the deceleration motor shaft 534 to perform worm-gear processing, the fabrication cost of the large-sized bearing 531 and the large-sized gear disk 532 is relatively high, thereby making the overall cost of the stopping position control motor system 5 for the sewing machine significantly increased. Accordingly, the problem to be solved here is to provide a motor system for a sewing machine, which can realize a first speed control, a second speed control and a stopping position control without having to use a decelerating motor, so as to reduce the overall cost of the motor system for the sewing machine.